The present invention relates to an electron emitting device for emitting electrons based on a principle of electric field emission, and in particular to an electron emitting device having a vacuum-sealed structure which operates as a vacuum tube, a display or the like.
In recent years, a fine working technique used in the field of forming an integrated circuit or a thin film has remarkably pushed the progress of a technique for manufacturing an electric field emission type electronic element for emitting electrons in a high electric field. In particular, the technique makes it possible to manufacture an electric field emission type cold cathode having a quite small structure. This type of electric field emission type cold cathode is an element of a fundamental electron emission device composing a triode type very small electron tube or electron gun. The electron source of this type of electric field emission type cold cathode has been known in some technical reports such as a report of "C. A. Spindt et. al. Journal of Applied Physics of Stanford Research Institute, vol. 47, No. 12, pp. 5248 to 5268 (December, 1976) and is disclosed in U.S. Pat. No. 3,789,471 assigned to C. A. Spindt, et. al. and U.S. Pat. No. 4,307,507 assigned to H. F. Gray, et. al. A structure for sealing such an electron source as an electron tube in vacuum employs a molding technique for vacuum-sealing each one of electron emitting sources composing a cold cathode array in a self-matching manner, which has been published by Kawamura, et. al. of Shin-Nittetu, Ltd. (New Japan Steel, Ltd.) in the Fourth International Vacuum Microelectronics Conference: IVMC 91, Nagahama. Further, another structure has been proposed for accommodating an overall electrode structure in a vacuum vessel, which is disclosed in Japanese Patent Lying Open Nos. 58-205128 and 8-89488.
An electric field emission type electron tube is a vacuum-sealed electrode structure composed of a cold cathode array consisting of a plurality of electron emission sources each having a micron order, an electrode for picking up an electrode beam, formed on and electrically insulated from the cold cathode array, and an electron collect electrode formed on and electrically insulated from the electrode for picking up an electron beam. The electron tube is very short, small, light and thin electron emitting device which serves to very efficiently operate at a large output.
And, as a structure required for sealing the electrode structure in vacuum, the following are mentioned.
(1) It has to keep a stable and high vacuum. As a first cause, if another kind of atoms are even slightly absorbed on the electron emission surface of the electron emitting source, the work function on the electron emission surface greatly changes, thereby making an electron emitting characteristic unstable. As a second cause, if gas is left in the electron tube, the emitted electron beam serves to ionize part of the left gas. The ions are accelerated by means of voltages applied between the cold cathode array (cathode) and the electrode for picking up an electron beam (gate) and between the cold cathode array (cathode) and the electron collect electrode (anode). The accelerated ions with high energy collide with the electron emitting source and are sputtered. This makes the rest of the cold cathode array shorter and the electron emission unstable.
(2) The vacuum vessel has to be as small as possible in a manner to make such a dimensional characteristic of the electrode structure very short, small, light and thin.
However, the molded structure for isolatedly sealing in vacuum a plurality of electron emitting sources composing the cold cathode array in a self-matching manner makes the dimension of the device very short, small, light and thin. Since each (or some) of the electron sources is sealed in vacuum, on the other hand, the residual gas or the gas emitted from the inner wall of the sealed area is variable in the sealed areas. The variety makes the circumstance different so that the operating characteristic for each vacuum-sealed electron emitting source is made uneven. As another sealed structure, it is possible to use such a type of vacuum-sealed structure as disclosed in Japanese Patent Lying Open Nos. 58-205128 or 3-89438, which has been widely used. However, with this structure, the dimension of the device is defined by the size of the vacuum vessel for accommodating the electrode structure. This eliminates the advantage of very short, small, light and thin electrode structure. After the electrode structure is accommodated in the vacuum-sealing vessel, the lid is fixed on the vessel by means of low-melting point glass or metal serving as a sealing member (adhesive agent). The sealing member is melted by applying heat. The application of the heat results in generating gas, thereby being unable to keep high vacuum sealing. As a remedy for this, a getter member may be provided in the vacuum vessel. This remedy, however, makes the dimension of the vacuum vessel larger.